It's not weird, there's a good reason for it. As I mentioned in a previous comment, its because the milks with a longer shelf life are UHT pasteurized, which uses higher temperatures for a shorter period of time than traditional pasteurization. They are typically labeled "ultra pasteurized." This extends the shelf life of milk.

Additionally, any time you see milk that is shelf stable (doesn't require refrigeration until opened) its been UHT pasteurized and packed in special aseptic packaging.

And, yes, I've noticed that, for some reason, organic milk tends to be UHT pasteurized more often than non-organic milk.